The present invention relates to lasers and pertains particularly to a modulation system for high frequency modulation of lasers.
Many different types of lasers have been developed in recent years. These different types of lasers have many different characteristics and each are suitable for particular special applications. Many of the lasers, because of their peculiar characteristics are more adaptable to certain applications than others.
Certain applications such as communications, require the ability to modulate the laser. The modulation may be either amplitude modulation (AM) or frequency modulation (FM). Frequency modulation of the carrier wave is preferred in communication systems because of its better signal to noise ratio as compared to amplitude modulation.
Injection lasers are one type of laser that is suitable for communication and other similar systems. These lasers are typically modulated by a modulation of the lasers bias current. The problem with this approach, however, is that the modulation rates are typically limited to rates below eight gigahertz. Modulation rates greater than this become difficult because of steady roll off of the achieved modulation depth or modulation index in the case of AM or FM modulation respectively. This type of laser bias modulation is called "internal" modulation.
It is therefore desirable that an improved system of modulation for lasers be available.